Dissolved loads/flux

Dissolved Load Fluxes at the Ebro Basin Scale. 106... 

Keywords Carbonate dissolution, Dissolved flux, Dissolved load, Ebro River basin, Evaporite dissolution, Long-term fluxes... 

The main purpose of this work was to estimate, over a long time period (more than 20 years), the export fluxes for dissolved loads on the catchment scale of the Ebro River basin. Data were compiled from the databank of the Confederation Hidro-grafica del Ebro (CHE), the Spanish government agency in charge of managing... 

As discussed elsewhere in this volume, another field where the use of U-series disequilibria has proven to be very useful is the study of chemical transport in waters, either marine (see Cochran and Masque 2003 Henderson and Anderson 2003), estuarine (Swarzenski et al. 2003) or continental waters. In the continental domain, in addition to characterization of transfer processes related to groundwater flows (Porcelli and Swarzenski 2003), radioactive disequilibria have also helped in constraining chemical exchanges between particulate, dissolved and colloidal loads of waters, as well as the origin of chemical fluxes carried by waters. 

Any compartment of the aquatic ecosystem can be represented as a particular volume containing water, particulate matter, biota, dissolved materials, etc. Loadings and exports are represented as mass fluxes across the boundaries of the volume element (processes Se, D and L). Reactive processes are treated as point processes centered within the volume. Thus, the EXAMS model takes into account both physical and chemical processes that affect the environmental fate of a particular chemical. 

The relative proportions of the total exported dissolved flux at Tortosa from the main tributaries are illustrated in Fig. 6. The Ebro basin in its upper part (upstream Mendavia station) contributes to 16.5-28% of the total exported flux in Tortosa with a mean contribution of 22.4% over the studied period. The Cinca is the tributary that mainly contributes to the total exported load at Tortosa with a mean... 

As an example, Fig. 36.7 shows the current measured during the coating step of the ALP assay described above, in which 30 loadings have been selected to functionalise the microchannels. As can be seen in Fig. 36.7, the measured current exhibits a kind of peak shape, which results from the introduction of new sample solution at given time intervals. Indeed, each time the pump is activated, the current drops due to the induced fluid flux and the concomitant renewal of the reporter molecule (dissolved oxygen in the present case) at the vicinity of the electrodes. Once the pump is stopped, the current increases rapidly... 

To evaluate the net riverine influx of dissolved species to the ocean, the river load has to be corrected for sea salts transported via the atmosphere from the ocean to the continents and rained out mainly in coastal precipitation. Table 9.7 shows the average concentration of selected dissolved and particulate elements in rivers from Martin and Meybeck (1979), and the corresponding net fluxes corrected for sea-salt cycling from Martin and Meybeck (1979). The corrections of fluxes for cyclic salts and pollution are still debatable estimates (e.g., Holland, 1978 Maynard, 1981), and affect mainly the evaluation of the net flux of Na+ by perhaps as much as 20%. 

River waters carry both dissolved and suspended substances to the sea. The concentrations and absolute fluxes vary tremendously. The suspended solids load is largely a function of the flow in the river, which influences the degree of turbulence and thus the extent to which solids are held in suspension and resuspended from the bed, once deposited. Table 3 shows a comparison of average riverine suspended particulate... 

Sea water contains a much lower concentration of dissolved organic matter than river water. More than half of this dissolved organic load is of a humic nature. These dissolved organic acids tend to flocculate as the salinity increases (10). Hair and Bassett (11) have observed an increase in the particulate humic acid load of an estuary as one approaches the sea. Although no studies of the distribution of humic materials throughout an estuarine system have been performed, it would appear that estuaries and their sediments in particular, act as a major sink for the dissolved and particulate humic materials. Nissenbaum and Kaplan (12) have observed that terrestrial humic materials are not deposited at great distances from shore in the marine system. A study of the flux of particulate carbon through the Chesapeake Bay comes to a similar conclusion (13). 

Inorganic sulfur compounds are at a much lower concentration in surface waters than in the ocean. Nevertheless, rivers move a large amount of dissolved sulfate to the sea each year (Meybeck, 1987) and industrial activities and agriculture have added much to this flux. Typically estimates are perhaps a little less than a lOOTg(S) yr with additional loads of the same magnitude as those from industrial and agricultural sources. There is also some... 

Recently, the determination of Tc in mixed fission products by neutron activation was reported. " TcOj was separated from the bulk of fission products and other elements in dissolved nuclear fuel by an iron(IIl)-oxidc-hydrate precipitation. 1 he filtrate containing TcOj was loaded on an anion exchange resin and I c bonded on the resin was exposed to a neutron flux in a nuclear reactor for only one minute. The counting of the 539 keV y-rays of ° Tc was performed with a germanium detector and a multichannel analyzer. The minimum detectability was 0.3 pg Tc limited by resin impurities and capsule materials [27]. 

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